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Guide to Choosing & Using Porch & Deck Construction Fasteners InspectAPedia®  -     Deck & Porch Construction & Structural Fasteners Deck & Porch Post & Beam Connectors: steel post cap connectors, plywood post to beam cleats, other connectors Deck & Porch Railings, Code Requirements, Safety Poor Construction Details and Improper Connections Can Lead to Dangerous Collapse of Decks and Porches

Here we discuss critical safe-construction details for decks and porches, including avoiding deck or porch collapse and unsafe deck stairs and railings. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Also see our review of that book. Our page top photo shows a hybrid deck structure that encompasses a boat. No fasteners were found securing the boat to the deck however.

© Copyright 2010 Daniel Friedman, Steve Bliss, Wiley & Sons, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

A Quick Photo Guide to Steel Connectors Used in Deck Construction

As described in Best Practices Guide to Residential Construction: For the strongest connection of beam to post, place the support beam directly on top of the posts, rather than bolting them to the side, so the full load is transferred to the posts. To keep the post in place and to prevent any twisting or shifting, the connection should be reinforced with steel strapping, a steel connector, or a treated plywood cleat.In general, notching a 4x4 post will leave too little wood for an adequate connection. A double 2x beam can rest on a notched 6x6 post, as shown. For the strongest connection of joists to the support beam, the joists should sit on top of the beam.

For a more streamlined appearance, however, joist hangers are acceptable. Make sure the hangers and nails are approved by the manufacturer for use with the new types of pressure- treated wood (ACQ or ACZA) and fill all the holes in the hangers with properly sized nails. In general, nail into the joists with 1 1/2-inch joist-hanger nails and nail into the beam with 10d to 16d common nails, as specified by the hanger manufacturer.

Deck Joist & Beam Sizing Tables

Spans, sizes and spacings for deck joists and deck beams are shown in Tables 4-7 and 4-8 of Best Practices Guide to Residential Construction as well as in most carpentry texts and framing guides. Here we give a rough "rule of thumb" that will provide a reasonable guess at allowable deck joist spans for most lumber species and grades:

Rule of Thumb for Inspecting Deck Joist Spans: While it is by no means a substitute for a proper table of spans and sizes of framing lumber, home inspectors often use a quick and dirty "rule of thumb" to guess whether or not deck floor framing has been over-spanned when joists are spaced 16" on center.

[(Depth of the Framing Member) - 2 ] x 2 = rough deck joist span limit for Southern Yellow Pine.

Example:

If you see a deck framed with 2x8 pressure treated lumber (typically Southern Yellow Pine or SYP), spaced 16" o.c.,

(8" -2) x 2 = 12' = maximum allowable span for a generic "deck floor joist"

A look at an actual span table will show that depending on the wood species, the allowable spans for a 2x8 floor joists with 40 pound live load with deflection limit of span/360, ranges from 10'5" (Western red cedar) to 12'9"
(Doug fir-larch).

Guide to Selecting the Proper Deck & Porch Structural Fasteners, Screws, Nails, Lags, Bolts

New Wood Preservatives and Their Corrosion Effects on Fasteners

Our photo, left, shows three fasteners we have found used with steel joist hangers. This photo shows the heads of each of these fasteners. Because the new wood preservatives ACQ (alkaline copper quat) and copper azole contain significantly more copper than the older CCA-treated lumber, they are estimated to be two to four times more corrosive to metals and galvanized coatings than the CCA they are replacing. Hot dipped galvanized nails: At bottom is a 1.5" long hot-dipped galvanized nail made by Simpson, and discussed just below. This is the proper fastener to use with galvanized steel joist hangers. Drywall screws: In the middle is a 1.5" drywall screw. These screws are tempting to use because they are available, easy to install, do not require drilling. We have inspected decks constructed entirely using interior drywall screws for both decking and for structural connections and joist hangers. Do not do this. This is an improper fastener that will fail and risks catastrophic deck collapse. Stainless steel utility screws: At the top is a 1 1/4" stainless steel screw used by a contractor to secure joist hangers when building the deck shown at the top of DECK & PORCH CONSTRUCTION. Although this screw is also made by a company that makes structural fasteners, a quick look at the company's specifications for this screw revealed that the manufacturer specifically advised that this screw was not a structural fastener and should not be used with steel framing connectors. The contractor removed the screws and used the proper fasteners instead. Stainless steel, galvanized, as well as proprietary-coating surfaced construction screws for use with treated lumber are available and of course are fine if used as recommended. But not the two screws shown in this photo and removed from decks we inspected.

Most treatment manufacturers recommend that fasteners and hardware in contact with the new treated wood be stainless-steel, heavily coated hot-dipped galvanized, or proprietary fasteners tested and approved by the manufacturer.

Hot-Dipped Galvanized Nails for Treated Lumber Decking

Stainless Steel Nails & Screws for Decks in Wet/Humid Climates

In very wet or humid climates, or in areas subject to salt-water spray or deicing salts, stainless steel is the best choice. Stainless steel is also recommended for tropical hardwoods, which tend to cause staining with coated nails. Both types 304 and 316 stainless steel have been tested for use with the new wood preservatives ACQ and copper azole. Type 304 is suitable for above- ground applications. Type 316 is recommended in areas subject to salt or salt water.

Caution: Never use stainless steel in contact with galvanized steel, as the galvanized coating will quickly corrode. Where fasteners such as nails, bolts, or lags are in contact with metal connectors, use the same metal for both.

Proprietary Deck Screw or Nail Coatings

If using one of these fastener types, make sure that it is recommended by the manufacturer for the specific type of decking being installed.

Aluminum Deck Nails

Best Practices Guide to Residential Construction continues:

Do not use aluminum fasteners, connectors, or flashings in contact with pressure-treated wood. The copper-based waterborne preservatives will cause corrosion and premature failure.

Guide to Selecting the Proper Deck or Porch Floor Decking Fasteners

Whether using nails or screws, make sure to choose a product that is up to the task both structurally and aesthetically. In general, screws are more expensive to buy and install, but often they make for a neater job with fewer callbacks due to boards popping up. Construction adhesives specially formulated for treated wood may be used in conjunction with nails or screws.

Nails for Use with Deck Floors - Decking

If the decking is to be nailed, use either spiral-, twist-, or ring-shanked nails to resist pullout. When using pressure-treated wood, the fasteners should be either hot- dipped galvanized, meeting ASTM A153, or stainless steel Type 304 or higher (see “New Preservatives and Corrosion,” above).

Galvanized nails sometimes cause discoloration with redwood, cedar, and tropical hardwoods, so stainless steel is a safer choice with these materials. Aluminum nails are also an option for redwood or cedar, but they should not be used with pressure-treated wood.

The bigger the head, the better the hold-down power. At a minimum, use a casing nail, preferably a common. Some manufacturers sell special decking nails with a head size in between the two. For 5/4" decking use a 10d (3-inch) nail. For thicker decking use a 16d (3 1/2") nail.

Deck spans are shown in the table 4-4 of Best Practices Guide to Residential Construction

Screws for Use with Deck Floors - Decking

Power-driven screws are more expensive and a little slower to install, but they are the best choice since they do a better job of holding down the decking and are more easily removed for repairs. For treated wood, use either hot-dipped galvanized screws that meet ASTM A153, stainless-steel multipurpose screws, or specialty decking screws with proprietary coatings tested and approved for use with the new types of wood treatments.

Multipurpose screws have a thicker shank and courser thread than drywall screws, giving them greater strength and better holding power. Some specialized decking screws also have cutting nubs under the head for self-countersinking in wood. Others have special concave “pancake” heads for composite decking. The composite-decking screws leave a crisp hole in the decking surface without the typical pucker of excess material (mushrooming) around the screw head.

In addition to Phillips-head screws, decking screws come with square-drive and star-drive heads that allow higher torque driving without stripping the head.

Also see DECK COLLAPSE Case Study (collapse of a new code-approved deck) and DECK FLASHING LEAKS, ROT Case Study for an example of an older deck with rot and collapse due to improper construction and missing building flashing.

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Technical Reviewers & References

• InspectAPedia.com^® - Daniel Friedman
• Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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EXTERIORS of BUILDINGS
STRUCTURAL INSPECTIONS & DEFECTS
ADVANCED INSPECTION METHODS
AGE of a BUILDING - how to determine
BEST CONSTRUCTION PRACTICES GUIDE
CHIMNEY INSPECTION DIAGNOSIS REPAIR
Cracks, Checking or Splitting Beams & Log Homes
CRAWL SPACES
DECK & PORCH CONSTRUCTION
  Deck Piers & Posts
  Deck & Porch Connections to Building
  Deck Flashing at Building
  Deck & Porch Structural Fasteners
  Deck & Porch Steps or Stairs
  Deck & Porch Railings
DECK COLLAPSE Case Study
DECK FLASHING LEAKS, ROT Case Study
DEFINITIONS of Mobile Home, Doublewide, Modular, Panelized
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DISASTER BUILDING INSPECTION & REPAIR SAFEY
EARTHQUAKE DAMAGED FOUNDATIONS
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FRAMING DAMAGE, INSPECTION, REPAIR
FRAMING DETAILS for BETTER INSULATION
FRAMING DETAILS for DOUBLE WALL HOUSES
FRT PLYWOOD
LOG HOME GUIDE
PANELIZED CONSTRUCTION & KIT HOMES
MODULAR HOME CONSTRUCTION
MOBILE HOMES, DOUBLEWIDES, TRAILERS
MOISTURE CONTROL in BUILDINGS
NOISE / SOUND DIAGNOSIS & CURE
ROOFING INSPECTION & REPAIR
ROT, FUNGUS, TERMITES
  TERMITE SHIELDS vs TERMITICIDE
ROT, TIMBER FRAME
SINK HOLES

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
• Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Wiley.com and also at Amazon.com. See our book review of this publication.
• Manual for the Inspection of Residential Wood Decks and Balconies, by Cheryl Anderson, Frank Woeste (Forest Products Society), & Joseph Loferski, October 2003, ISBN-13: 978-1892529343, $39.00 at Amazon.com or at the InspectAPediaBookstore
• ...

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